Catalyst components for the stereospecific polymerization of olefins have been disclosed in the art. Ziegler-Natta catalysts may be used for such polymerizations and can comprise a solid catalyst component a magnesium dihalide, a titanium compound an internal electron donor compound and/or an alkyl aluminum (Al-alkyl) compound. However, when a higher polymer crystallinity of the polymer is desired, an external donor (for example, an alkoxysilane) may be needed in order to obtain higher isotacticity. Esters of phthalic acid, such as diisobutylphthalate, may be used as internal electron donors in catalyst preparations. The phthalates may further be used as internal electron donors in combination with alkylalkoxysilanes as external electron donors. This catalyst system may give good performances in terms of activity, isotacticity and xylene insolubility (XI).
However, one of the problems associated with the use of this catalyst system is that phthalates have recently raised concerns regarding potential health and medical issues associated with their use.
Consequently, research activities have been devoted to discovering alternative classes of internal electron donors for use in the preparation of catalyst components for propylene polymerization.
One of the classes investigated is acyloxyesters as described, for example in U.S. Pat. No. 7,351,778. These compounds may be obtained by the esterification of hydroxyl ester derivatives. Surprisingly, the applicant has found that a particular class of donors based on mercapto derivatives can generate a wide arrange of molecules with equal or different functional groups which, when used as internal electron donors, can generate catalysts showing a good balance of activity and stereospecificity.